Caffeine has a half-life of about five hours, in some people ten. How it disturbs sleep even if you fall asleep fine, how much per day is acceptable and how to place your last coffee correctly.
In short
- Caffeine blocks adenosine, which signals tiredness; the half-life is five hours on average.
- A coffee at 4 pm leaves half the caffeine in the blood at 10 pm; that reduces deep sleep even if you fall asleep.
- Up to 400 milligrams a day count as safe, that is three to four cups of filter coffee, in pregnancy 200.
- The last coffee eight to ten hours before bed, earlier for slow metabolizers.
How caffeine works
Over the day adenosine accumulates in the brain, a substance that signals tiredness and builds sleep pressure. Caffeine fits the same receptors and blocks them: the tiredness is not gone, it is no longer reported. That is why it returns as soon as the caffeine is broken down, often as an afternoon slump that triggers the next coffee.
The half-life
Caffeine is broken down in the liver with an average half-life of five hours. A coffee with 100 milligrams at 4 pm leaves 50 milligrams at 9 pm and 25 at 2 am. Some people break it down faster, others, genetically or because of the pill, hormonal changes or medication, need ten hours. Whoever falls asleep fine in the evening thinks they are insensitive; sleep studies show, however, that caffeine in the blood reduces deep sleep by up to 20 percent without you noticing. You sleep, just worse.
How much is acceptable
Up to 400 milligrams a day count as safe for healthy adults, in pregnancy 200. A cup of filter coffee has 80 to 120 milligrams, an espresso 60 to 80, a latte with two shots 130, black tea 40 to 60, green tea 30, cola 35 per 330 milliliters, an energy drink 80 to 160. Coffee is linked in studies with less cardiovascular disease, diabetes and liver disease; the problem is not the coffee but the timing.
Placing the last coffee
The rule of thumb: eight to ten hours before bed, so with an 11 pm bedtime at the latest at 2 pm. Whoever is sensitive or sleeps badly moves the limit to noon. The first coffee works best 60 to 90 minutes after getting up, once the morning cortisol has faded. In the afternoon decaf, which has 2 to 5 milligrams, herbal tea or a walk help against the slump.
Withdrawal and reset
Whoever drinks more than three cups and wants to halve it gets headaches and fatigue for two to four days. Reduce gradually, replace one cup with decaf every other day. After two weeks the morning cup works like it used to.
Try it
Caffeine CalculatorCoffee, espresso, tea, cola, energy drink with time: how much caffeine is still in your blood at bedtime, as a curve.Sleep CalculatorWhen do you have to get up? The best bedtimes by 90-minute cycles, or the other way round: when you should wake up.Longevity ScoreTwelve questions about sleep, movement, food, stress and habits: your estimated biological age and the three levers with the biggest effect.Frequently asked questions
Is decaf sleep-neutral?
Almost. It contains 2 to 5 milligrams per cup and the polyphenols of coffee. In the evening it is a good choice.
Why does coffee not wake me up anymore?
With high consumption the brain adapts and forms more adenosine receptors. The coffee then only keeps withdrawal away. Two weeks of reduction reset sensitivity.
What about matcha and green tea?
They contain caffeine plus L-theanine, which smooths the effect. The effect is gentler, the half-life the same. In the afternoon the time limit applies here too.
This article is general information and not medical advice. If you have symptoms or existing conditions, or before changing any medication, talk to your doctor.
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